It is often necessary or desirable to monitor various parameters of blood and to obtain quantitative data concerning such parameters in real time. In order to accomplish this, blood is caused to flow through a flow-through housing past sensors which provide signals representative of the parameters of interest. For example, Cooper U.S. Pat. No. 4,640,820 shows a flowthrough housing with fluorescent sensors which respond to the partial pressure of oxygen, the partial pressure of carbon dioxide and the pH of blood which has passed through the flow-through housing.
Prior to using the flow-through housing, the sensors must be calibrated. One calibration technique, which is used for the sensors of the Cooper patent, is to attach the sensor carrier to a calibration housing containing calibration liquid. This places the sensors in communication with a relatively large cross-sectional area passage. The gas or gases of interest are then bubbled through the calibration liquid. A similar technique is utilized to calibrate the sensors shown in Maxwell U.S. Pat. No. 4,830,013.
This calibration technique, which employs an essentially static calibration liquid, is most satisfactory when used in conjunction with sensors adjacent a passage of sufficient cross-sectional area so that the calibration liquid remains in the passage while the gases are passed through the liquid. Because the sensors must be kept wet, a gas-only calibration technique cannot be employed.
For some applications, it is desirable to utilize a flow-through housing having a relatively small cross-sectional area and to maintain that area sterile during calibration. In fact, the cross-sectional area is sufficiently small so that, when gas is passed through the liquid, the surface tension may cause the calibration liquid to be expelled from the passage and prevent exposure of the sensors to the gases in the calibration liquid and thus cause an inaccurate calibration.